Spotting equipment generally can be considered to be apparatus that matches sequentially presented items to a corresponding sequence of other items in a predetermined geometrical relationship with one another, i.e. registration. For example, spotting apparatus is useful in matching labels to boxes or applying flexible wrappings (i.e. wraps) to containers or boards, and the like. The terms "label" and "wrap" as used herein, sometime interchangeably, is not intended to be limited to a sheet or notice or that is inscribed or printed with information or a pattern, but in a broader sense, simply identifies a sheet of material that may have any particularly desired flexibility or stiffness, so as to include board wrappings and the like.
There are a number of prior art systems that examine objects such as containers or labels optically for a number of purposes, that can be used to automatically register labels with corresponding containers and spot the properly registered label on a surface of the box or vice-versa. For example, U.S. Pat. No. 3,778,618 (Laskowski) shows an apparatus for detection of transparent or translucent sheets passing on a conveyor wherein an opaque flap is disposed so as to be movable by the leading edge of a sheet as the latter is carried by a light transmissive conveyor belt into the path of light and detected by a photosensor, thereby identifying the position of that leading edge. The release of the flap from the trailing edge of the sheet results in detection of the position of the trailing edge by the photosensor. Because the system only detects the positions of those pans of the leading and trailing edges engaged with the flap, the information obtained is highly limited. Thus, where the leading and trailing edges of the sheet are not normal to the direction of travel of the conveyor, or the sheets are randomly oriented on the conveyor, the information obtained by the photodetector is necessarily incomplete, ambiguous and will not serve adequately to provide precise registration based on that information.
U.S. Pat. No. 4,750,035 (Chang et al.) discloses apparatus for video inspection of containers to determine quality, cleanliness and the like, wherein light is projected through transparent or translucent containers moving on a conveyor and captured on CCD video cameras to provide multiple views of the entire expanse of the sides of the containers from different angularly spaced positions. The different views of the same container are then compared with one another, a data processor correlates the images to analyze for defect patterns and defective containers are rejected.
U.S. Pat. Nos. 4,682,023 (Yoshida), 4,943,713 (Yoshida), 5,216,239 (Yoshida) and 5,095,204 (Novini) are of interest as showing inspection means using light and a light-sensitive element such as a photosensor or video camera to detect defects in the bottoms of light transmissive containers.
Information for registration can be predetermined by nesting the wrap and/or the object in preformed cavities or nests in or on the conveyor belt, but such nests necessarily limit the system to specific forms and sizes of wrap and object and the system therefore lacks flexibility of use. Further, such nesting would not ordinarily provide any information as to misfit items that may fit the nest poorly or are incorrectly oriented.
To effect reasonably adequate registration, for example between a wrap or label and an object such as a box, requires detailed knowledge of the size, shape and orientation in at least two dimensions of the wrap and object. Such information with respect to the wrap and object can readily be provided by optical viewing means such as electronic camera means that view the wrap and/or object being carried on conveyor means and provide digitized images suitable for processing in a digital computer as in the prior art. However, whether or not the prior art equipment uses a single camera or two cameras, it suffers from a number of problems, particularly where one wishes to provide adequate data, not only for inspection, but to provide reasonably precise registration between, for example, a label and a box. Although data as to size, shape and orientation can often be obtained from determination of the outlines of the label and box as by cameras, if the conveyor surfaces on which the labels and boxes are carried do not contrast sufficiently with the latter, the information provided either to the camera or to a computer processing the camera output may be inadequate or incomplete. For example, even the use of high intensity illumination reflected from the label and surface of the conveyor belt may not prove efficacious if the color and albedo of the label and the conveyor belt are very close, because the signal-to-noise ratio will tend to be very poor.
A principal object of the present invention is therefor to provide a spotting system that overcomes the above-identified problems of the prior art. Yet other objects of the present invention are to provide such as system in which the signals generated by a camera viewing a conveying surface and items supported thereon are optimized; to provide such a system in which such optimization is effected by increasing the optical contrast between the conveyor surface and an item carried thereon so that the signal-to-noise ratio of signals provided by the camera is increased; and to provide such a system that is relatively inexpensive and is capable of high speed operation.